Input Impedance Of Antenna Research Articles

The Effect of Human Tissue on Field Strength Measurements In Vivo Using a Resonant UHF Cavity-Backed Slot Antenna.

An inward-looking wearable antenna can be used for radio communications with internal transceivers in vivo. The radio transmissions are recorded using an array of electric field sensors on the skin. This paper reports the effect of living tissue on a small cavity-backed slot antenna pressed onto soft tissue of the human torso at 2.09 GHz. In-vivo measurements were made on the skin surface at 13 torso locations using eight participants (age range, 22-68 years old), with body mass indexranging between 20.3 and 31.6 kg/m2 . Ultrasound imaging was used to determine the skin and fat thickness at every measurement location. The variation in the antenna input impedance measurements demonstrated that the human tissues (fat and muscle) affect the antenna impedance but the mismatch creates field strength measurement errors of less than 2 dB. Fat thickness in the range of 3-30 mm can slightly degrade the performance of these wearable antennas. These effects can be partly mitigated by selective location and antenna retuning to improve transceiver communications. Bioelectromagnetics. 2021. © 2021 Bioelectromagnetics Society.

The Induced EMF Method as an Alternative to the Iterative Method for the Approximation of the Reflection Coefficient on Thin Wires

One way to find an analytic approximation of the input impedance of thin wire antennas is to make an educated guess of the current distribution, which is then used for the induced electromotive force (EMF) method. This method is frequently described in the literature and yields accurate results. In this article, it is shown that this method can be used to approximate the transmission line reflection coefficient while including high-frequency effects. It is, hence, applicable to smaller wave lengths than the classical transmission line theory. Two general problems are considered: 1) the infinite wire with a lumped impedance above ground and 2) the semi-infinite wire with an arbitrary port configuration above ground. For both configurations, the reflection coefficient is approximated using the induced EMF method. An important intermediate step is to find exact equations that relate the input impedance and the reflection coefficient. The results are compared to an exact solution and an iterative one, which is used in recent publications. It is shown that the induced EMF method is a good alternative to the iterative method. The novelty of this article is the utilization of the induced EMF method for the analytic approximation of the transmission line reflection coefficient and linking the input impedance and the reflection coefficient.

Improved Discrete-Time Boundary Condition for the Thin-Wire FDTD Analysis of Lossy Insulated Cylindrical Antennas Located in Lossy Media

For the thin-wire (TW) finite-difference time-domain (FDTD) analysis of lossy insulated antennas surrounded by lossy media, an improved discrete-time boundary condition (DTBC) at the interface is proposed here. In previous TW-FDTD techniques, the DTBC formulations on the material discontinuity between the lossy insulation and lossy surrounding media were derived from the dielectric constitutive relation under the uniform field approximation (UFA) over each time step. In this paper, to achieve higher accuracy, an improved DTBC is formulated from Maxwell’s equations under the linear field approximation (LFA) and subsequently corrected in the TW-FDTD update equation. By comparing the input impedances of Teflon-insulated cylindrical monopole antennas located in wet soils, we show that the proposed approach provides higher accuracy than previous techniques.

Design of Circular Polarized Patch Antenna for NaviC Receiver Applications

In this paper, a circular polarized patch antenna at NaviC and S-band is presented for Indian Regional Navigational Satellite System (IRNSS) receiver applications. For this application proposed antenna is satisfying the criteria of circular polarisation with a bandwidth of 2477 MHz to 2508 MHz. The shape of proposed antenna exhibits good gain which is required for the good operation of communication systems for IRNSS. Antenna is operating at frequency of 2492.08 MHz (S-band) with a return loss better than -15 dB and has the stable radiation pattern. For designing of this antenna a conducting patch of 27.5 mm x 27.5 mm and a FR-4 material with thickness of 1.6 mm and dielectric constant of 4.3 is used as a substrate material. In addition to this, the antenna is fed with a coaxial feed technique and matched with 50 Ω input impedance of antenna. The parameters like radiation pattern, VSWR, E field, gain and axial ratio are analysed and achieved by CST studio Suite.

Dependence of the Input Resistance of Vibrator and Microstrip Antennas on the Primary Field

The dependence of input impedances of vibrator and microstrip antennas on the profile of the primary field is investigated using the analytical inversion of the main hypersingular operator and the explicit form of the inverse integral operator. General patterns in the behavior of input resistances for arbitrary primary fields were found. Numerical calculations were performed and agreement with theoretical results has been obtained.

60 GHz wide‐band psi (Ψ)‐shaped long‐wire antenna for wireless on‐board chip‐to‐multi‐chip communication

A novel type of wide-band long-wire antenna is presented for 60 GHz wireless on-board chip-to-multi-chip applications using a vertically polarised electric field. The psi-shaped structure is devised to match the antenna input impedance to 50 Ω and to increase the front-to-back ratio by placing two bent 0.5λeff lines parallel to the original long-wire antenna, which resulted in improved realised gain and can be directivity compared to those of a conventional baseline structure. The psi-shaped long-wire antenna shows a peak gain of 10.2 dBi, an end-fire gain of 7 dBi, a 22% impedance bandwidth (52–65.2 GHz), and a 25.8% 3 dB gain bandwidth (56–74 GHz) in an area of 3.1 × 105 mm2. This study presents the proposed antenna for an on-board chip-to-multi-chip communication scenario for a distance of 20 mm, with a peak transmission gain of −19.5 dB and a 3 dB bandwidth of 11.8 GHz (=19.6%), which ranges from 55.4 to 67.2 GHz.

Effect of Induced Electromotive Force on a VLF Linear Antenna in an Anisotropic Plasma

In this article, the effect of an induced electromotive force (EMF) on the electrical characteristics of a linear antenna in an anisotropic ionosphere over a very low-frequency (VLF: 3–30 kHz) range is investigated. By establishing a technically sound mathematical model of a linear antenna with a motional status relative to the geomagnetic field, the induced EMF effect on the current distribution and input impedance of a linear antenna is first systematically analyzed and quantified. A 3-D kernel function is obtained to match the EMF generated on an arbitrarily oriented antenna. Computations show that as the dip and azimuth angles of an antenna vary in a wide range, the fluctuations on the input impedance always remain within 10%, with the change mainly reflected on the real part. The discrepancy caused by an induced EMF will be more significant when the antenna length reaches 1 km, which should not be ignored for long antennas. This analysis aims to mitigate the undesired effects led by an induced EMF and may provide heuristic support for practical schemes of VLF space-borne applications.

Low-Profile High-Directivity Circularly-Polarized Differential-Fed Patch Antenna With Characteristic Modes Analysis

A low-profile high-directivity circularly polarized patch antenna is proposed in this article. Two orthogonal slots are etched out in the middle of a square patch. As a result, radiation patterns of original TM12/21 modes are reshaped to the desired ones that are similar to those of TM10/01 modes, leading to significant enhancement of broadside radiation. To accommodate the modified current distributions of the two operating modes, a pair of perturbed stubs is proposed and then loaded on the slot-loaded patch, which leads to the quadrature-phase difference. In order to suppress unwanted modes that tilt the radiation pattern away from broadside direction, differential-fed configuration instead of single-fed one is adopted to excite modified TM12/21 modes. Characteristic modes theory (CMT) is used to analyze the input impedance of differential-fed patch antenna and determine the two feeding positions. Next, the proposed antenna is compared with three conventional ones, which reveals its superiority in the highest directivity. Besides, it is also discussed how to determine the size of the finite ground plane. We find that the size of 1.5λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 1.5λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> can increase directivity slightly and effectively prevent radiation pattern from tilting tendency. Finally, a prototype antenna is fabricated and measured for validation.

Analysis of a hybrid fractal curve antenna using the segmentation method

AbstractA microstrip‐fed hybrid Fractal antenna for WLAN application is presented in this article. The proposed antenna is composed of meander and Koch elements combined to form a longer curve that extends the electrical length. This approach simultaneously reduces the operating frequency and antenna size. The Green's functions and segmentation method are used to calculate the input impedance of the hybrid Fractal antenna. For analysis, the amalgamated antenna shape is decomposed into simple regular segments. The impedance parameters of the newly arranged shapes are calculated by the corresponding Green's functions. The impedance matrix equations of all the segments are presented so as to display in a single matrix whose solution determines the input impedance of the complete antenna geometry. To validate the theory, a prototype of the proposed antenna has been numerically simulated and experimentally measured.

High-Resolution Dielectric Constant Measurement Using a Sensor Antenna With an Allocated Link for Data Transmission

A dual-band low-profile patch antenna, which operates based on aperture-coupling mechanism, is exploited to measure the permittivity of a sample under test (SUT) in the microwave frequencies and send the measured data simultaneously. The upper resonant frequency, which is considerably affected by changing the permittivity of the SUT, can be utilized for sensing purpose. In contrast, the lower resonant frequency is almost independent of the samples hence can be used as the communication link. The samples are placed on top of the feeding side of the structure. The variation in the sample’s permittivity leads to changes in the input impedance of the sensor antenna. While this change results in having different feedline-dependent resonant frequencies, the cavity-dependent resonant frequency is almost preserved intact for different samples. The sensor antenna is designed using electromagnetic solver and an equivalent circuit is proposed to model its behavior. The effect of varying parameters in the equivalent model is investigated. Moreover, by fabricating the sensor, the measurement results show that by changing the permittivity of samples from 1 to 12.85, the upper band resonant frequency (feedline-dependent) shifts from 12.30 to 11.37 GHz (78 MHz per unit dielectric constant). Nevertheless, the small variation in resonant frequency and radiation characteristics of the antenna in the lower band (cavity-dependent) can provide a stable communication channel with respect to the SUT. This link with a reasonable 2.8% (9.54-9.81 GHz) 10-dB impedance bandwidth can be reserved for sending the measured and pilot data in a wireless sensor system.

New compact of absorber thermal surface

Frequency-selective heat infrared (IR) detectors are promising for numerous new apps such as solar cell detection, gas analysis, multi-color imaging, multi-channel detector, recognition of artificial objects in a natural setting, but these features involve extra filters which lead to elevated costs. Plasmonic metamaterial absorbers (PMAs) can impart frequency selectivity to standard heat, IR detectors merely by regulating the absorber surface geometry to generate surface plasmon resonance at the desired frequency. We present a nanoantenna-based mid-infrared absorber for heat infrared detectors. Our structure uses a portion of the noble metal used in standard absorbers and is only one layer thick, which enables incredibly tiny thermal conductivity leading to possibly very low thermal detector noise. Simulation results show that the proposed nanoantennas can achieve a harvesting efficiency of 40% at a frequency of 150 THz where the antenna input impedance is matched to that of fabricated rectifying devices. Achieve maximum bandwidth Absorber from 100 to 200 THz for application purposes energy harvesting sensor.

Restoration of antenna performance in the vicinity of metallic cylinder in implantable scenario

In this study, the authors propose an innovative solution based on mantle cloaking method to restore the performance of an implantable antenna, which is degraded due to the scattering from an adjacent metallic body. In an implantable device, the metallic body is generally used as a house for electronic circuitry. Initially, they investigate the deteriorating effects of metallic body on the antenna input impedance and radiation characteristics. Finally, by covering the metallic body with the designed metasurface, most of the antenna parameters are successfully retrieved. The proposed model is fabricated and measured with the in vitro test by immersing the antenna inside a muscle emulating gel, as well as, inside the minced pork.

A new approach to nearly constant input impedance of self-complementary antennas

Conformal techniques, based on the covariance of Maxwell's electrodynamics under the full conformal group in four spacetime dimensions, are discussed in relation with the constant input impedance properties of frequency-independent antennas. In particular, we show that by applying suitable conformal transformations to existing self-complementary planar structures like logarithmic spirals, the constant input impedance property is considerably improved, especially in the low-frequency domain, where it usually fails due to the large wavelength involved. This procedure enables to perform a more intelligent truncation with the aim to capture some of the properties left behind in the cutting and to design realistic ultra wideband antennas with a more controlled value of the input impedance in the whole operation range.

Wideband Circularly Polarized Antenna Using Single-Arm Coupled Asymmetric Dipoles

This article presents a novel design concept to realize a wideband circularly polarized (CP) antenna by using single-arm coupled asymmetric dipoles (SCADs). First, an impedance compensation method is developed to obtain flat antenna input impedance by designing different arm lengths of the asymmetric dipole. Then, a single-arm coupling method is introduced to improve the antenna bandwidth. Four asymmetric dipoles are bent and sequentially coupled to each other among the long arms of the dipoles. By elaborately adjusting the coupling among the long arms, improved bandwidth and compact radiator size are achieved simultaneously. In addition, to further enhance and optimize the operating bandwidth of the antenna implementation, impedance matching strip and interdigital structure are introduced into SCADs. To verify the design concept, a prototype of the SCAD antenna was designed, fabricated, and measured. Experimental results agree well with the simulations, showing a wide impedance bandwidth of 108% (1.53-5.12 GHz) and an axial ratio (AR) bandwidth of 96% (1.78-5.06 GHz). To the best of our knowledge, the proposed design concept of SCADs is first used to design a wideband CP antenna. Both the simulated and measured results prove that the proposed antenna is a promising candidate for modern broadband CP applications.

New Design of Cylindrical Rectangular Microstrip Antenna (CRMA) By Using The Slots Technique

A conformal antennas are plays an important role due to its multitasking possibilities , which have many opportunities in several applications. In this study, a new design of cylindrical rectangular microstrip antenna(CRMA ) excited at mode, was achieved in order to operate at the frequency of 5.6GHz. The simulation was done by Finite Difference Time Domain(FDTD) method using MATLAB program. The input impedance, return loss and radiation pattern of antenna were calculated and plotted. By using the slots technique and dual-layers substrate technique , the bandwidth(BW) is increased to 88.88% . Also BW is increased as the dielectric constant value is decreased.

Analysis of dual-band matching of an ends-fed dipole-like antenna and a coaxial line

The problem of dual/multi-band radiation of a single-body antenna is of a great topicality today when there is a continuing development of wireless communications both for civil and military purposes. The estimation of dual-band performance of endsfed dipole-like radiator, in particular, its matching with a standard purely active resistance coaxial line is given in the paper. The focus was on stating the necessary conditions and requirements on the geometric sizes of the structure under investigation and the frequency range it have to be analyzed through. It is also considered how to decrease amount of calculations needed at the starting stage of the antenna designing that includes the exact analytical approaches for near field calculations. This decrease is based on the difference in the impact the parameters under consideration have on the antenna input impedance. For the crucial electrodynamics characteristics calculations the induced electromotive forces (EMF) method is used, which has established itself as one of the most convenient in this field.

Compact broadband circularly polarized UHF RFID tag antenna for metallic mounting

ABSTRACT We report a broadband ultra-high frequency (UHF) radio frequency identification (RFID) tag antenna of compact size mounted on a metallic object in a near field communication (NFC) RFID system. One half of the square radiation patch has a semi-annular strip feedline embedded inside a semicircle-shaped slot to improve the antenna bandwidth and gain, and the other half of the radiation patch has an L-shaped slot and a shorting pin to increase the circular polarization (CP) bandwidth and reduce the antenna size. The resonant input impedance of the tag antenna can be tuned easily by varying the length of the semi-annular feedline, and the gap between the feedline and the etched semicircular slot. The proposed tag antenna has a wide measured impedance bandwidth (−10-dB |Γ|) covering the whole operating frequency range of 181 MHz (from 790 to 971 MHz) for a UHF RFID system. The measured 3-dB axis ratio (AR) bandwidth is 43 MHz (from 895 to 938 MHz), which is much larger than those of the CP tag antennas reported in the literature for metallic objects. Further experiment has shown that the proposed tag antenna can provide a stable reading range when mounted on metal plates of various sizes.

Frequency Domain Method for Scattering Damping Time Extraction of a Reverberation Chamber Based on Autocorrelation Functions

The scattering damping time (τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> ) of a reverberation chamber is a very important parameter but hard to obtain accurately. A novel method for extracting this parameter is presented in this article. By utilizing the frequency domain autocorrelation function and the unstirred frequency domain autocorrelation function, τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> can be directly calculated from measured S-parameters without the need of performing the inverse Fourier transform (IFT). Mathematical derivation is given based on the Wiener-Khinchin theorem, and experimental measurements are conducted for different frequency bands as well as different stirrer configurations to verify the proposed approach. Compared with the conventional IFT-based method, the proposed method does not involve the procedure of manually selecting the fitting range, while still maintains advantages in terms of the independence of the radiation efficiency and input impedance of the measurement antennas.

Circularly Polarized Implantable Antenna With Improved Impedance Matching

This letter proposes a circularly polarized patch antenna with a compact volume of 91.9 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> for implantable applications. Foremost, the input impedance of patch antenna with reduced ground inside lossy muscle tissue is analyzed. Then following the traditional way of realizing circular polarization (CP) performance, crossed slots are introduced into the patch center. However, as the working environment is lossy tissue rather than traditional air, additional LC elements are needed to meet the impedance matching of 50 Ω. Thus, besides crossed slots in the center, arc-shaped slots and shorting pins are loaded on the antenna edge. Simulated results show that a CP bandwidth of 18.3% is obtained, proving the antenna is suitable for biomedical devices.

Estimating an Error of the Excitation-Field Model in the Form of a Delta Function in the Theory of Dipole Antennas

We compare the values of the input impedance of a linear dipole antenna, which are obtained on the basis of solving integral equations by the exact and approximate methods. The expansions in terms of the weighted Chebyshev polynomials and trigonometric functions are used for solving the equations with exact kernels. The results obtained by our own methods are compared with those obtained using the well-known MMANA code, which is based on solving the integral equation with the approximate kernel and the delta-function model. The dependences of the input impedance on the primary-field distribution are studied theoretically and numerically. The errors resulting from replacing the exact kernel with an approximate one are determined.